Adolescents are increasingly using novel flavored tobacco products (i.e., hookah, little cigars, and electronic cigarettes), the health risks of which may include earlier initiation and added risk for initiation of other drugs. Aggressive marketing of novel flavored tobacco products targeting adolescents is likely to blame for the widespread, rapid adoption of these products; perhaps through ensuing perceptions of reduced harm. Risk perceptions, especially those of lower risk, have a demonstrated predictive relationship with tobacco use among adolescents. Still, gaps in scientific evidence include 1) the impact of marketing on adolescents' perceptions of novel flavored tobacco products; 2) how changes in novel flavored tobacco products-related perceptions influence adolescent initiation and use progression; and 3) how use of novel flavored tobacco products influences initiation and use progression of traditional and unflavored tobacco products and other drugs, including patterns of co- and poly-use. We will determine the relationships between novel flavored tobacco product-related marketing and changes in perceptions and use, and subsequent initiation and use progression of traditional and unflavored tobacco products and other drugs, including trajectories of co- and poly-use. Findings will elucidate the complex interactions of factors influencing novel flavored tobacco product initiation and use progression, including initiation and trajectories of co- and poly-tobacco or other drug use, or both. Adolescents are at greatest risk for drug use and translating this evidence into effective drug-use prevention and treatment interventions for them would greatly improve public health and reduce suffering. Secondary analysis of longitudinal data from an ongoing four-year school-based cohort study (N = 786) designed to examine the relationships among perceptions of risks and benefits, marketing, and youth tobacco use and addiction will be used. Participants are students from ten large and diverse high schools across California who are assessed every six months from baseline to study conclusion. Aim 1 will determine relationships between novel flavored tobacco product-related marketing and adolescent perceptions by comparing levels of perceived risk by level of marketing exposure over time. Aim 2 will determine how novel flavored tobacco products-related perceptions influence initiation and use progression by controlling for baseline level of perceived risk and comparing rates of initiation and use progression over time. Aim 3 will determine relationships between novel flavored tobacco product use and traditional and unflavored tobacco- and other drug-use initiation and progression including trajectories of co- and poly-use using path analysis to estimate the importance of hypothesized predictive relationships.